Schottky barriers conductive polymers

Currently, much work is devoted to the synthesis of conducting polymers for use in a variety of applications. Polyacetylene, the prototype conducting polymer, has been successfully demonstrated to be useful in constructing p-n heterojunctions, (1) Schottky barrier diodes, (2,3) liquid junction photoelectro-chemical solar cells, (4) and more recently as the active electrode in polymeric batteries. (5) Research on poly (p-phenylene) has demonstrated that this polymer can also be utilized in polymeric batteries. (6)... 

Since protection of electrodes against corrosion in the photoelectrolysis cells is a question of vital importance, many attempts have been made to use protective films of different nature (metals, conductive polymers, or stable semiconductors, eg., oxides). Of these, semiconductive films are less effective since they often cause deterioration in the characteristics of the electrode to be protected (laying aside heterojunction photoelectrodes specially formed with semiconducting layers of different nature [42]). When metals are used as continuous protecting film (and not catalytical "islands" discussed above), a Schottky barrier is formed at the metal/semiconductor interface. The other interface, i.e., metal/electrolyte solution is as if connected in series to the former and is feeded with photocurrent produced in the Schottky diode upon illuminating the semiconductor (through the metal film). So, the structure under discussion is but a combination of the "solar cell" and "electrolyzer" within the photoelectrode Unfortunately, light is partly lost due to absorption by the metal film. 

In diodes, the conducting polymer (usually a p-type semiconductor) is in contact with an n-type semiconductor or a metal. In the former case a heterojunction can form at the interface, while in the latter case a Schottky barrier can be created. The relation between the current density and the voltage is described by Richardson s equation [217] ... 

Nalwa HS (ed) (1996) Handbook of organic conductive molecules and polymers, vol 2 and 3. WUey, New York, NY Nalwa HS (ed) (1997) Handbook of organic conductive molecules and polymers, vol 4. Wiley, New York, NY Nguyen VC, Potje-Kamloth K (1999) Electrical and chemical sensing properties of doped polypyrrole/gold Schottky barrier diodes. Thin Solid Films 338 142-148... 

Potje-Kamloth K (2001) Conducting polymer-based Schottky barrier tmd heterojunction diodes and their sensor application. In Nalwa HS (ed) Handbook of surfaces tmd interfaces of materials, vol 5. Academic, San Diego, CA, pp 445-494... 

In view of the above, conductivity measurements were conducted in asymmetric systems Au-polymer-Si for polystyrene and polysilazane, and Au-polymer-In for polysiloxane. The difference in barrier height between Au-polymer and Si-polymer estimated on the basis of measurements of the Au-Si barrier is ca. 0.5 eV (M) which, in the case of the conductivity limited by the electrodes, should produce a difference in the intensity of the currents of opposite polarizations equal to about 8 orders of magnitude. The difference in work function of Au and In, on the other hand, is ca. 1 eV so, on the assumption of the Schottky mechanism of conductivity, the difference in the intensity of opposite polarizations should amount to 17 orders of magnitude ( ). As can be seen in Fig. 4 in the case of an asymmetric polysilazane sample there is a difference in the intensity of the currents although this difference does take the expected course, it is several times smaller than expected, and is thus virtually negligible. A similar result was obtained for the polystyrene sample, while in the case of the asymmetric system based on polysiloxane there was no difference in the intensity of the opposite-biassed fields over the entire range of fields used - up to 3 x 10 V/m. It can thus be assumed that the conductivity in the films under study is dominated by the Poole-Frenkel volume generation independent of the contact effects. Such were also the conclusions of the workers who studied the conductivity in polystyrene (29) and polysiloxane (21). 

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